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Abstract:

Methods for small cell discovery in heterogeneous networks are proposed
for efficient cell search and better power saving. In one novel aspect, a
user equipment (UE) measures small cells only when the UE enters into the
vicinity of the small cells. For example, the UE detects the proximity of
small cells and reports proximity indication information to the network.
Based on the vicinity indication, the network provides suitable
measurement configuration for small cells. In a second novel aspect, the
UE performs guided search for small cell discovery. In a third novel
aspect, the UE increases search rate for small cells when it is in the
vicinity of small cells, and decreases search rate for small cells when
it is not in the vicinity of small cells. The detection may be based on
location information provided by the network or based on vicinity
detection information autonomously stored by the UE.

Claims:

1. A method, comprising: determining whether a user equipment (UE) is in
vicinity of a small cell in a mobile communication network; changing
mobility measurements of the UE based on said determination.

2. The method of claim 1, further comprising: transmitting proximity
indication information to a base station, wherein the proximity
indication information includes at least a carrier frequency of the small
cell; receiving measurement configuration information from the base
station for the small cell; and performing measurements over the carrier
frequency of the small cell.

3. The method of claim 1, further comprising: receiving cell ID
information, about one or multiple neighbor small cells, from the base
station such that the UE can detect and identify the small cells faster
and with less battery consumption.

4. The method of claim 1, further comprising: receiving location
information from the base station such that the UE can determine whether
the UE moves into the vicinity of the small cell.

5. The method of claim 4, further comprising: receiving frequency
information about the small cells, or reference to measurement objects
configured for the UE, such that the UE can search for the small cells.

6. The method of claim 4, wherein the location information contains radio
signal parameters of neighboring cells related to coverage of the small
cell.

7. The method of claim 4, wherein the location information contains a
geographical area configuration based on latitude and longitude.

8. The method of claim 1, wherein the determining is based on vicinity
detection information autonomously stored by the UE, and wherein the
small cell is not a closed subscriber group (CSG) cell.

9. The method of claim 8, wherein the UE stores the vicinity detection
information only for cells that the UE has received a signaling
indication that the UE may store said information.

10. The method of claim 8, wherein the stored vicinity detection
information contains a location of the small cell and/or the radio signal
measurements of neighboring cells of the small cell.

11. The method of claim 1, further comprising: increasing search rate for
small cells if the UE is in vicinity of the small cell; and decreasing
search rate for small cells if the UE is not in vicinity of the small
cell.

12. A user equipment (UE), comprising: a cell vicinity-detection module
that determines whether a user equipment (UE) is in vicinity of a small
cell in a mobile communication network; a transmitter that transmits
proximity indication information to a base station, wherein the proximity
indication information includes at least a physical cell ID and a carrier
frequency of the small cell; a receiver that receives measurement
configuration information from the base station for the small cell; and a
measurement module that performs measurements over the carrier frequency
of the small cell.

13. The UE of claim 12, wherein the receiver receives cell ID information
about one or multiple neighbor small cells from the base station such
that the UE can identify the small cell.

14. The UE of claim 12, wherein the receiver receives at least location
information from the base station such that the UE can determine whether
the UE moves into the vicinity of the small cell.

15. The UE of claim 14, wherein the receiver receives at least frequency
information about the small cells, or reference to measurement objects
configured for the UE, such that the UE can search for the small cells.

16. The UE of claim 14, wherein the location information contains at
least a location of the small cell and coverage information of
neighboring cells of the small cell.

17. The UE of claim 12, wherein the determining is based on vicinity
detection information autonomously stored by the UE, and wherein the
small cell is not a closed subscriber group (CSG) cell.

18. The UE of claim 17, wherein the UE stores vicinity detection
information only for cells that the UE has received a signaling
indication that the UE may store said information.

19. The UE of claim 17, wherein the stored vicinity detection information
contains a location of the small cell and coverage information of
neighboring cells of the small cell.

20. The UE of claim 12, wherein the UE increases search rate for small
cells if the UE is in vicinity of the small cell, and wherein the UE
decreases search rate for small cells if the UE is not in vicinity of the
small cell.

21. A method, comprising: receiving measurement configuration from a base
station by a user equipment (UE) in a mobile communication network,
wherein the measurement configuration includes measurement object
configured for a preferred cell with at least cell ID and location
information; applying proximity detection on whether the UE is in
vicinity of the preferred cell based on the location information; and
performing measurements for the preferred cell based on the measurement
configuration.

22. The method of claim 21, wherein the location information contains at
least a GPS location of the preferred cell and radio signal parameters of
neighboring cells related to coverage of the preferred cell.

23. The method of claim 21, wherein the UE continues to perform
measurements for the preferred cell when the radio signal
strength/quality of a serving cell is better than a stop-measurement
threshold.

24. A method, comprising: receiving measurement configuration from a base
station by a user equipment (UE) in a mobile communication network;
applying proximity detection on whether the UE is in vicinity of a
preferred cell; and performing measurements based on a measurement rate
configured via the measurement configuration, wherein the UE increases
the measurement rate for the preferred cell if the UE is in vicinity of
the preferred cell, and wherein the UE decreases the measurement rate for
the preferred cell if the UE is not in vicinity of the preferred cell.

25. The method of claim 24, wherein the proximity detection is based on
vicinity detection information autonomously stored by the UE, and wherein
the stored vicinity detection information contains at least a location of
the preferred cell, coverage information of neighboring cells of the
preferred cell, and RF fingerprint information of the preferred cell.

26. The method of claim 24, wherein the proximity detection is based on
location information from the base station, and wherein the location
information contains at least a GPS location of the preferred cell and
radio signal parameters of neighboring cells related to coverage of the
preferred cell.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. §119 from
U.S. Provisional Application No. 61/522,578, entitled "Method for Small
Cell Discovery in Heterogeneous Network," filed on Aug. 11, 2011, the
subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The disclosed embodiments relate generally to heterogeneous
networks, and, more particularly, to small cell discovery in
heterogeneous networks.

BACKGROUND

[0003] E-UTRAN is the air interface of 3GPP's Long Term Evolution (LTE)
upgrade path for mobile networks. In E-UTRAN mobile networks, the network
controls a UE to perform measurement for intra/inter-frequency or
inter-RAT mobility by using broadcast or dedicated control. For example,
in RCC_IDLE state, a UE shall follow the measurement parameters defined
for cell reselection specified by the E-UTRAN broadcast. On the other
hand, in RCC_CONNECTED state, a UE shall follow the measurement
configurations specified by measurement objects via radio resource
control (RRC) messages directed from the E-UTRAN.

[0004] Intra-freq measurement occurs when the current and the target cell
operate on the same carrier frequency. In such a scenario, UE should be
able to carry out measurements without measurement gaps. This is because
UE receiver is able to measure reference signals of neighboring cells
while simultaneously performing data communication with serving cell in
the same frequency. On the other hand, inter-freq measurement occurs when
the target cell operates on a different carrier frequency as compared to
the current cell. Similarly, inter-RAT (Radio Access Technology)
measurement occurs when the target cell operates on a different RAT as
compared to the current cell. In such a scenario, UE may not be able to
carry out measurements without measurement gaps. This is because UE
receiver needs to switch to another frequency to perform measurements and
then switch back to the frequency of the current cell to perform data
communication.

[0005] Current LTE mobile networks are typically developed and initially
deployed as homogeneous networks using a macro-centric planning process.
A homogeneous cellular system is a network of macro bases stations in a
planned layout and a collection of user terminals, in which all the macro
base stations have similar transmit power levels, antenna patterns,
receiver noise floors, and similar backhaul connectivity to the packet
core network. LTE-Advanced (LTE-A) system improves spectrum efficiency by
utilizing a diverse set of base stations deployed in a heterogeneous
network topology. Using a mixture of macro, pico, femto and relay base
stations, heterogeneous networks enable flexible and low-cost deployments
and provide a uniform broadband user experience. In a heterogeneous
network, smarter resource coordination among base stations, better base
station selection strategies and more advance techniques for efficient
interference management can provide substantial gains in throughput and
user experience as compared to a conventional homogeneous network.

[0006] In heterogeneous networks, small cell discovery is important to
ensure efficient offload from macrocells to small cells. A small cell may
include a picocell, a femtocell, or even a microcell. Because of the
relative small cell coverage, inter-frequency measurement time maybe too
long for small cells. For example, depending on the measurement gap
pattern, inter-frequency cell identification time could be up to 7.68s,
which is unacceptable for small cell discovery. Furthermore, UE may waste
power if it keeps trying to search for small cells that are in spotty
deployment. Note that, measurement gap may be unnecessary for UE equipped
with multiple RF receiver modules. However, for such multi-RF UE, power
wasting is still a concern. Therefore, it is desirable to identify and
evaluate strategies for improved small cell discovery, especially for the
purpose of inter-frequency mobility. The support in 3GPP specifications
for closed subscriber group (CSG) cells, which are assumed to be small,
has significant drawbacks for networks where a UE may visit large number
of small cells, as it relies on the UE storing significant amounts of
information for each individual cell where the UE is allowed access.

SUMMARY

[0007] Methods for small cell discovery in heterogeneous networks are
proposed for efficient cell search and better power saving. In one novel
aspect, a user equipment (UE) measures preferred small cells only when
the UE enters into the vicinity of the small cells. For example, the UE
detects the proximity of small cells and reports proximity indication
information to the network. Possible parameters of the proximity
indication information may include the entering or leaving the vicinity
of a small cell, the cell ID, and the carrier frequency of the small
cell. Based on the vicinity indication, the network provides suitable
measurement configuration for one or more small cells. The suitable
measurement configuration involves configuration items that affect the
search performance of small cells, to ensure that UE search for small
cells is quick enough. For example, more frequent searching for small
cells are used when UE is in the vicinity of small cells, and less
frequent searching for small cells are used when UE is not in the
vicinity of small cells.

[0008] In a second novel aspect, the UE performs guided search for small
cell discovery. The UE receives measurement configuration for preferred
small cells with cell ID and location information. The UE applies
proximity determination on whether the UE enters vicinity of the
preferred cell based on the location information. The UE then performs
measurements for the preferred cell based on the measurement
configuration if the UE is in vicinity of the preferred cell. In one
example, the UE continues to perform measurements for the preferred cell
even when the RSRP of a serving cell is better than a stop-measure (e.g.,
s-measure) threshold.

[0009] In a third novel aspect, the UE increases search rate for small
cells when it is in the vicinity of small cells, and decreases search
rate for small cells when it is not in the vicinity of small cells. The
detection may be based on location information provided by the network or
based on vicinity detection information autonomously stored by the UE.
The location information and the stored vicinity detection information
contain location (e.g., Latitude and longitude), coverage information
(e.g., radio parameters such as signal strength) of a neighbor cell,
and/or cellular "RF finger-print".

[0010] Other embodiments and advantages are described in the detailed
description below. This summary does not purport to define the invention.
The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.

[0012]FIG. 1 illustrates a method of small cell discovery in a mobile
communication network in accordance with one novel aspect.

[0013]FIG. 2 illustrates a first embodiment of small cell discovery in
accordance with one novel aspect.

[0014]FIG. 3 illustrates a second embodiment of small cell discovery in
accordance with one novel aspect.

[0015]FIG. 4 illustrates a third embodiment of small cell discovery in
accordance with one novel aspect.

[0016]FIG. 5 illustrates a fourth embodiment of small cell discovery in
accordance with one novel aspect.

[0017]FIG. 6 illustrates a fifth embodiment of small cell discovery in
accordance with one novel aspect.

[0018]FIG. 7 is a flow chart of one embodiment of small cell discovery in
accordance with one novel aspect.

[0019]FIG. 8 is a flow chart of a method of guided search for small cell
in accordance with one novel aspect.

[0020]FIG. 8 is a flow chart of one embodiment of UE autonomous search
and measure for small cell in accordance with one novel aspect.

DETAILED DESCRIPTION

[0021] Reference will now be made in detail to some embodiments of the
invention, examples of which are illustrated in the accompanying
drawings.

[0022]FIG. 1 illustrates a method of small cell discovery in a mobile
communication network 100 in accordance with one novel aspect. Mobile
communication network 100 is a heterogeneous network comprising a
plurality of macro base stations eNB 101-103, a plurality of pico base
stations 104-106, and a user equipment UE 110. Macro base stations
101-103 serve macrocells 111-113 over a first carrier frequency f1
respectively. Pico base stations 104-106 serve picocells 114-116 over a
second carrier frequency f2 respectively. In the example of FIG. 1,
macrocells 111-113 are referred to as normal cells or large cells, while
picocells 114-116 are referred to as small cells or preferred cells.
Small cells in general have much smaller cell coverage as compared to
macrocells. Examples of small cells include picocells, femtocells, or
microcells.

[0023] For mobility management, UE 110 periodically measures the received
signal power and quality of its serving cell and neighboring cells and
reports the measurement result to its serving eNB for potential handover.
For example, Reference signal received power (RSRP) or Reference signal
received quality (RSRQ) measurement of a cell helps to rank between the
different cells as input for mobility management. Inter-freq measurement
occurs when the target cell operates on a different carrier frequency as
compared to the current serving cell. In the example of FIG. 1, UE 110 is
served by serving eNB 103 in cell 113 over carrier frequency f1. UE 110
may not be able to carry out measurements over carrier frequency f2
without measurement gaps. This is because the receiver on UE 110 needs to
switch to carrier frequency f2 to perform measurements and then switch
back to carrier frequency f1 to perform data communication. Depending on
the measurement gap pattern, inter-frequency cell identification time may
take as long as 7.68 s.

[0024] In a heterogeneous network, however, the cell size of a macrocell
and the cell size of a small cell can be very different. While the
inter-frequency measurement time may be acceptable for macrocells, it may
be too long for small cells such as picocells. For example, the size of a
macrocell typically ranges from one to 20 kilo-meters, while the size of
a picocell typically ranges from four to 200 meters. Therefore, it is
probably too long for UE 110 to be able to discover picocell 116 during
the configured gap time as the target cell when UE 110 moves within the
cell coverage of picocell 116. Furthermore, when UE 110 is located far
away from any picocell, UE 110 may waste power if it anyway tries to
search for small cells.

[0025] In one novel aspect, UE 110 only searches for small cells under
certain conditions (e.g., based on location information). In one example,
UE 110 first obtains physical cell ID (PCI) information from serving eNB
103 such that UE 110 can identify small cells from macrocells (step 1).
At location L1, UE 110 is not in vicinity of any small cell and does not
search for small cell (step 2). When UE 110 moves into the vicinity of
picocell 116 at location L2, UE 110 detects and reports the proximity of
picocell 116 to eNB 103 (step 3). Based on the vicinity indication, eNB
103 sends UE 110 measurement configuration for picocell 116 (step 4).
Based on the measurement configuration, UE 110 is then able to
efficiently measure picocell 116 accordingly (step 5).

[0026]FIG. 1 also illustrates a simplified block diagram of UE 110. UE
110 comprises memory 121 containing program instructions and databases, a
processor 122, a radio frequency (RF) module having a transmitter and a
receiver, an antenna 124 for transmitting and receiving radio frequency
signals, a measurement module 125 for performing radio signal
measurements, and a cell vicinity-detection module 126 for detecting
proximity of small cells. The various modules are function modules and
may be implemented by software, firmware, hardware, or any combination
thereof. Each base station comprises similar function modules. The
function modules, when executed by processors 122 (e.g., via program
instructions contained in memory 121), interwork with each other to allow
UE 110 to detect and report the proximity of small cells, to receive
measurement configuration for small cells, and to perform measurements
and report measurement result of small cells to its serving eNB for
proper handover decisions.

[0027]FIG. 2 illustrates a first embodiment of small cell discovery in
accordance with one novel aspect. In step 211, UE 201 receives
information broadcasted by eNB 202 via system information block (SIB)
carried in a broadcast channel (BCH). The broadcasted information
contains physical cell ID (PIC) information of different cells in the
network. For example, PCI split information may be used to identify
picocells by a specific PCI range (e.g., some specific PCI values are
specifically allocated for picocells). In step 212, eNB 202 requests UE
201 to report the proximity of picocells. For example, eNB 202 sends an
RRC message (e.g., Proximity request) to UE 201. In step 213, UE 201
detects the proximity of picocells when it moves into the vicinity of
picocells. In step 214, UE 201 reports the proximity of picocells via
proximity indication information. Possible parameters of the proximity
indication information may include the entering or leaving the vicinity
of a picocell, the cell ID, and the carrier frequency of the picocell.
Based on the reported proximity indication information, in step 215, eNB
202 sends measurement configuration to UE 201 for the picocell. The
measurement configuration typically includes the cell ID and the carrier
frequency of the picocell to be measured. In step 221, UE 201 performs
measurements for the picocell accordingly. Finally, in step 222, UE 201
reports the measurement result (e.g., RSRP and/or RSRQ of the picocell)
back to eNB 202.

[0028] Under the first embodiment, UE 201 measures picocells only when
picocells are nearby. Because picocells are assumed to be in spotty
deployment, such method has better power saving. However, UE 201 must be
able to detect the proximity of picocells without any assistance from the
network. For example, UE 201 may visit picocells before and stores
related information (e.g., RF fingerprint) to enable the later proximity
detection.

[0029]FIG. 3 illustrates a second embodiment of small cell discovery in
accordance with one novel aspect. In step 311, UE 301 receives
information broadcasted by eNB 302 via system information block (SIB).
The broadcasted information contains physical cell ID (PIC) information
of different cells in the network. For example, PCI split information may
be used to identify picocells by a specific PCI range. In addition, the
broadcasted information may also contain location information of the
picocells. In step 312, UE 301 detects the proximity of picocells when it
moves into the vicinity of picocells based on the PCI and the location
information. In step 313, UE 301 reports the proximity of picocells via
proximity indication information. Possible parameters of the proximity
indication information may include the entering or leaving the vicinity
of a picocell, the cell ID, and the carrier frequency of the picocell.
Based on the reported proximity indication information, in step 314, eNB
302 sends measurement configuration to UE 301 for the picocell. In step
321, UE 301 performs measurements for the picocell accordingly. In step
322, UE 301 reports measurement result (e.g., RSRP and/or RSRQ of the
picocell) back to eNB 302. Finally, in step 323, based on the measurement
result, eNB 302 sends a handover command to UE 301.

[0030] Under the second embodiment, UE 301 measures picocells only when
picocells are nearby. Because picocells are assumed to be in spotty
deployment, such method has better power saving. Furthermore, UE 301 is
able to detect the proximity of picocells under the assistance from the
network, e.g., using the location information sent from eNB 302. For
example, the location information may include radio signal parameters
related to coverage of a picocell, and/or a geographical area
configuration of the picocell based on latitude and longitude. To be able
to fully utilize such location information, UE 301 may have GNSS
capability.

[0031]FIG. 4 illustrates a third embodiment of small cell discovery in
accordance with one novel aspect. In step 411, UE 401 and eNB 402
communicate with each other over an established RRC connection. In step
412, eNB 402 sends measurement configuration to UE 401. The measurement
configuration contains measurement objects configured for small cells
over certain carrier frequencies, as well as PCI and location information
of the small cells. Each measurement object contains a set of measurement
parameters (e.g., Time-to-Trigger (TTT) values, L3 filtering parameters,
measurement bandwidth, etc.) for a specific carrier frequency. The
measurement configuration is done by RRC message in RRC_Connected state.
In step 413, UE 401 detects the proximity of small cells when it moves
into the vicinity of one or several small cells based on the PCI or other
information, such as location information and RF fingerprints. In step
421, UE 401 performs measurements for the detected small cells based on
the measurement configuration received in step 412. In step 422, UE 401
reports measurement result (e.g., RSRP and/or RSRQ of the small cells)
back to eNB 402. Finally, in step 413, based on the measurement result,
eNB 402 sends a handover command to UE 401.

[0032] Under the third embodiment, UE 401 performs guided search for small
cell discovery. The measurement configuration and location information
(guidance from the network) for small cells is done ahead of time. Upon
UE 401 entering into the vicinity of the small cells, UE 401 starts to
measure the small cells. Similar to the second embodiment, UE 401
achieves better power saving because UE 401 measures small cells only
when small cells are nearby. UE 401 is also able to detect the proximity
of small cells using the location information provided by eNB 402, under
the working assumption that UE 401 is equipped with GNSS capability.
Under the guided search approach, the small cells are sometimes referred
to as preferred cells. This is because the purpose of measuring and
discovering the small cells is for traffic offloading, which is typically
preferred for improved spectrum efficiency.

[0033] Typically, when the RSRP level of the serving cell is above a
threshold value specified by s-Measure, UE stops measuring the signal
qualities of neighbor cells, as measurements of neighbor cells are no
longer necessary for mobility management purpose. Therefore, for power
saving, a parameter to stop UE's measurement activity (e.g., s-Measure)
is sometimes used to reduce the frequency of UE'smeasurements. For small
cell discovery, however, the checking condition of s-Measure no longer
applies for preferred cells because the purpose is for traffic
offloading. As a result, the UE tries to measure preferred cells even if
the RSRP of the current serving cell is above the s-Measure threshold
value.

[0034]FIG. 5 illustrates a fourth embodiment of small cell discovery in
accordance with one novel aspect. In step 511, UE 501 and eNB 502
communicate with each other over an established RRC connection. In step
512, eNB 502 sends measurement configuration to UE 501. The measurement
configuration contains measurement objects configured for certain carrier
frequencies, as well as PCI and optionally location information of small
cells. In step 513, UE 501 detects the proximity of small cells when it
moves into the vicinity of one or several small cells based on the PCI or
other information, such as location information and RF fingerprints.
Alternatively, UE 501 may apply vicinity determination based on
autonomously stored vicinity detection information. In step 521, UE 501
performs measurements for the detected small cells. In step 522, UE 501
reports measurement result (e.g., RSRP and/or RSRQ of the picocell) back
to eNB 502. Finally, based on the measurement result, eNB 502 sends a
handover command to UE 501.

[0035] Under the fourth embodiment, UE 501 uses vicinity knowledge to
change search/measurement performance and how often it performs search
for small cells. For example, when UE 501 determines that it is near one
or several preferred small cells, it increases the rate of searching for
such cells (e.g., by increase measurement frequency in step 521), as
compared to normal search rate for macrocells (e.g., measurement objects
configured in step 512). On the other hand, when UE 501 determines that
it is not near one or several preferred small cells, it decreases the
rate for searching for such cells (e.g., by decrease measurement
frequency), as compared to normal search rate for macrocells. By
dynamically adjusting search rate depending on vicinity knowledge, UE 501
can perform small cell discovery more efficiently.

[0036]FIG. 6 illustrates a fifth embodiment of small cell discovery in
accordance with one novel aspect. In step 611, UE 601 is in connected
mode and eNB 602 requests UE 601 to indicate when UE 601 is in the
vicinity of preferred neighbor cells (e.g., via proximity request
message). In step 612, eNB 602 sends measurement configuration to UE 601.
The measurement configuration contains measurement objects configured for
cells (e.g., macrocells) over certain carrier frequencies, as well as PCI
and optionally location information of preferred cells. In step 613, UE
601 detects the proximity of picocells when it moves into the vicinity of
one or more preferred cells based on the PCI or other information, such
as location information and RF fingerprints. Alternatively, UE 601 may
apply vicinity determination based on autonomously stored vicinity
detection information. In step 614, UE 601 reports the proximity of the
detected preferred cells via proximity indication information. Possible
parameters of the proximity indication information may include the
entering or leaving the vicinity of a preferred neighbor cell, the cell
ID, and the frequency bands of the neighbor cell. Based on the reported
proximity indication information, in step 615, eNB 602 configures a
suitable measurement configuration for preferred cells. In step 616, eNB
602 sends measurement configuration to UE 601 for preferred cell
measurements. In step 621, UE 601 performs measurements for the preferred
cells accordingly. In step 622, UE 601 reports the measurement result
(e.g., RSRP and/or RSRQ of the preferred cells) back to eNB 602. Finally,
in step 623, based on the measurement result, eNB 602 sends a handover
command to UE 601.

[0037] The suitable measurement configuration involves configuration items
that affect the search performance of small cells, to ensure that UE
search for small cells is quick enough. In one embodiment, eNB configures
different parameter sets for macrocells and small cells in a measurement
object. In another embodiment, eNB configures a set of parameters for
small cells in a measurement object. Those small cell specific parameters
(e.g., shorter TTT) can further enhance the robustness of mobility. For
example, more frequent searching for small cells are used when UE is in
the vicinity of one or several preferred small cells. On the other hand,
when UE determines that it is NOT in the vicinity of one or several
preferred small cells, it may indicate this explicitly to the network.
Alternatively, the UE no longer indicates vicinity information, and the
network can interpret the absence of such indication as non-vicinity. As
a result, the network can ensure that the UE has a suitable measurement
configuration involving less frequency searching for small cells.

[0038] In order for UE to measure preferred cells, UE needs to have
vicinity detection information ahead of time. In one embodiment, UE can
autonomously learn and store the vicinity detection information. UE
decides to store information about a cell, that the cell is preferred for
searching, when the UE has found this cell or the UE is served by this
cell. For example, the preferred cell broadcasts certain information,
e.g., an explicit indication meaning that "this is a preferred cell for
autonomous search", or "this is a picocell type". In another example,
another cell (e.g., an inter-frequency macrocell) had indicated that
cells on certain frequency bands shall/may be treated as preferred cell
for which autonomous search is allowed, recommended, or requested. The
macrocell may also provide additional information on how to identify the
preferred cells, e.g., via split PCI range information.

[0039] After identifying the preferred cells, UE then stores the vicinity
detection information of the preferred cells. The vicinity detection
information may include information based on GPS location, based on being
in coverage of another cell, or based on detecting a cellular "RF
finger-print"--a combination of being in coverage of certain cells (maybe
on different frequencies), mobility measurement being in certain range,
and/or timing measurements.

[0040] In another embodiment, UE can rely on network assistance to obtain
and store the vicinity detection information. For example, the serving
eNB provides explicit information that in a certain geographical area,
higher performance search (e.g., frequent searching) shall be applied.
The geographical area being defined in terms of cell ID, radio parameters
(e.g., signal strength) related to coverage of neighboring cells, or in
terms of Latitude and Longitude. Such location information is typically
provided to UE by RRC measurement configuration.

[0041]FIG. 7 is a flow chart of one embodiment of a method of small cell
discovery in accordance with one novel aspect. In step 701, a user
equipment (UE) determines whether the UE is in vicinity of a small cell
in a mobile communication network. In one example, the proximity
determination is based on location information received from the network.
In another example, the proximity determination is based on vicinity
detection information autonomously stored by the UE. The location
information and the stored vicinity detection information contain
location (e.g., Latitude and longitude), coverage information (e.g.,
radio parameters such as signal strength) of a neighbor cell, and/or
cellular "RF finger-print" information. In step 702, the UE transmits
proximity indication information to a base station, and the proximity
indication information includes a cell ID and a carrier frequency of the
small cell. In step 703, the UE receives measurement configuration for
the small cell from the base station. For example, the measurement
configuration may contain small cell-specific measurement performance
requirement or measurement parameters. In step 704, the UE performs
measurements for the small cell.

[0042]FIG. 8 is a flow chart of a method of guided search for small cell
in accordance with one novel aspect. In step 801, a user equipment (UE)
receives measurement configuration from a base station in a mobile
communication network. The measurement configuration includes measurement
objects configured for a preferred cell with cell ID and location
information. In step 802, the UE applies proximity detection on whether
the UE enters vicinity of the preferred cell based on the location
information. In step 803, the UE performs measurements for the preferred
cell based on the measurement configuration if the UE is in vicinity of
the preferred cell. In one example, the UE continues to perform
measurements for the preferred cell even when the RSRP of a serving cell
is better than a stop-measure threshold.

[0043]FIG. 9 is a flow chart of one embodiment of a method of UE
autonomous search and measure for small cell in accordance with one novel
aspect. In step 901, a user equipment (UE) receives measurement
configuration from a base station in a mobile communication network. In
step 902, the UE applies proximity determination on whether the UE enters
vicinity of a preferred cell. In step 903, the UE performs measurements
based on a measurement rate (i.e., search rate) configured via the
measurement configuration. If the UE is in vicinity of the preferred
cell, then the UE increases the measurement rate for the preferred cell.
On the other hand, if the UE is not in vicinity of the preferred cell,
then the UE decreases the measurement rate for the preferred cell.

[0044] The proposed small cell discovery method can be applied for idle
mode mobility management as well. For example, UE can obtain the small
cell configuration or measurement parameters via eNB broadcasting
messages or eNB unicasting messages when UE leaves RRC Connected state.
With such small cell information, UE can perform cell
selection/reselection onto small cells with priority. In one example, an
idle-mode UE searches for a small cell with higher measurement frequency
when it moves within the vicinity of the small cell.

[0045] Although the present invention is described above in connection
with certain specific embodiments for instructional purposes, the present
invention is not limited thereto. Accordingly, various modifications,
adaptations, and combinations of various features of the described
embodiments can be practiced without departing from the scope of the
invention as set forth in the claims.

Patent applications by Per Johan Mikael Johansson, Kungsangen SE

Patent applications by Yih-Shen Chen, Hsinchu City TW

Patent applications by MEDIATEK INC.

Patent applications in class Control or access channel scanning

Patent applications in all subclasses Control or access channel scanning